There are federal laws that prohibit the possession, sale, and consumption of marijuana. And I've actually heard people say - including, I might add, lawyers (which is extremely troubling to me) - that people don't have a Constitutional right to legally possess and consume marijuana.
But those people have it backwards. The question should be, show me in the constitution the article or amendment which grants to the federal government the power to say one cannot! Unless there's some article or amendment enumerated in the U.S. Constitution that grants to the federal government the power to prohibit such a thing, then such a law should be ruled as unconstitutional.
I'm neither a lawyer nor an activist for the legalization of marijuana, but if it required an amendment (the 18th) to the U.S. Constitution to grant the federal government the power to outlaw the sale and possession of liquor (intoxicating substances), then why shouldn't it take a similar amendment to give them similar power to make law regarding a similar substance?
The 18th amendment, by the way, was repealed by the passage of the 21st amendment fourteen years later.
http://en.wikipedia.org/wiki/Eighteenth_Amendment_to_the_United_States_Constitution
This is an illustration as to why I think people misunderstand the real intent of the U.S. Constitution, and why I think its intent has been trampled upon. And I'm baffled as to why courts over the years have ruled as constitutional those laws which clearly are not!